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Anybody ever feel they geared their diffs too low?

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Ned Kelly

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Anyone ever feel they regeared their street and trail truck too low?
I'm asking in regards to using an old school 3speed non-overdrive auto like a TH350 or TH400 trans (with NP205)....yep, I'm still driving something from the last century!:doah:
 
I did mine 4.88, and have had to drive in 3rd (1 to 1) for a lot of miles with a head wind. tach with converter unlocked was in the 3600-3800 rpm 65ish mph, makes great power here.

You would be fine with 4.10 to 4.56 33 to 35" tire respectively
 
37’s with a th350 and 4.88’s. Around town was fine but 70mph on the highway was like 4500rpm or something ridiculous. With the 4L80e I’m swapping in I’m kinda wishing I had done 5.13’s because of the tall first gear but we will see.
 
use to run a th350/205 with 4.10 and 38" swampers . didnt do to bad at all ...... but there was a built 400 sbc under the hood feeding it and it was STRONG
 
Ned Kelly said:
Anyone ever feel they regeared their street and trail truck too low?
I'm asking in regards to using an old school 3speed non-overdrive auto like a TH350 or TH400 trans (with NP205)....yep, I'm still driving something from the last century!:doah:
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It depends on tire size and use of the truck.
I had a '72 K5 with 37s, SM465 and 4:56 gears. I could drive 70 mph to Moab at 3100 rpm no problem, it just used more gas.
My '70 K10 has 4:56 with a 700R4. It was fine with the 33's. I haven't driven it much on the interstate with the 35s, though.
 
Wes Harden said:
5.33's with .7 od = 3.73, the .75 in the 4l80e would be 3.99 @centexk5
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It’s the first gear I’m concerned with. 2.48 in the 4l80 vs 2.52 in the th350. It’s a small difference but I’ve read some grumbling about it. Hopefully the additional 200+hp and torque and 2200rpm stall converter will help.
 
centexk5 said:
It’s the first gear I’m concerned with. 2.48 in the 4l80 vs 2.52 in the th350. It’s a small difference but I’ve read some grumbling about it. Hopefully the additional 200+hp and torque and 2200rpm stall converter will help.
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If anyone can tell the difference there, I would bet that it's the torque converter stall.
 
You’d be surprised how deeply you can gear a truck and it still feel normal. We have all driven trucks with poorly matched gears and tires. I don’t feel like it’s unreasonable to say that the majority of 4wd owners have done that so much it’s made under geared trucks feel adequate. We all know that 3.08’s and 35’s are WRONG but there’s always guys that’ll argue that they drove a truck like that trouble free for 45 years - they’re just so used to the fact that it works that they no longer realize it’s a pig.

My Blazer has a 4spd with 5.86 gears, it started with 43’s but I recently swapped to 40 Boggers. The truck feels absolutely normal to drive up to 55 or so, any faster and it gets around 3k rpm so you begin to feel it work. I wouldn’t run it on the interstate but it’s fine around town.

Once upon a time, there was a member here named tvguy / Steve. Steve was local to me and had an 80’s Dodge crew cab with a 4spd, 6.17’s and 35” Boggers. I road in this truck many times and it was fine, it was really frisky in traffic but it never felt like you were driving around in 4 low.

Don’t fear the gear.
 
I geared mine to what stock rpm was at 75mph to a 02 Silverado.

But this is LS engine and overdrive trans with 35s and 4.56 gears
 
I forgot to add that my 5.86’s and 40’s are very close to 4.10’s and 30’s which is an average 3/4 ton set up.
 
muddybuddy said:
I think more people regret not going with more gear the first time vs thinking they have too much gear.
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I agree with this, nothing worse than doing it twice. I think people need to be realistic with what they're actually going to use the truck for and what they are comfortable with. If its more trail than street by all means go with a little more gear but if you hit the trails once a month and drive it everyday then go with a little less, be honest with yourself. I see a million lifted Jeeps with one ton axles that have never left blacktop :surepal: A lot of times people forget that when these trucks were new they had 31ish tires and 4.10s with no overdrive so you're turning some RPMs on the highway, people got used to overdrive and now they think its "screaming" when it gets up in RPM a little.
 
Yeah, all good points guys. I liked the input.
True, when you think of it, some factory OEM K30 came with 31" tires, 4sp, and 4.56 gears. So correct, you can't really grossly overgear.
I'd love a 4l80e but just not going to happen at this point. As mentioned also, after driving a modern 4sp OD (or more), a 3sp auto seems like Ford Model A technology, but it is still respectable and ok (just a fuel user).
 
I don't own a truck with overdrive, 2 4 speeds and a TH400 and they all get the job done, and I'm not on the side of the road when a sensor craps out.
 
There's always a doubler, which lets you run huge tires with medium-range gears and OD-like highway RPMs. To get the full effect you'd have to shift ranges on the street, which is sort of more complicated than driving a manual, even though you have an auto. Maybe somebody who's tried it can chime in.
 
Blue85 said:
There's always a doubler, which lets you run huge tires with medium-range gears and OD-like highway RPMs. To get the full effect you'd have to shift ranges on the street, which is sort of more complicated than driving a manual, even though you have an auto. Maybe somebody who's tried it can chime in.
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Mine is doubled with a 203/205 with 4.10s and 37s, SM465

Shifting the 203 while moving is a guessing game, like shifting a manual w/o a clutch


It works fine without using the case like a splitter. I need 3rd and a half gear, or an nv4500 with 4.88s to get the RPMs just right on the hard climbs at high altitude. Engine is 420hp and 406 lb/ft
 
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